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Connecting an encoder to S7-1200

Created by: Pyrus at: 3/2/2016 8:25 PM (48 Replies)

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3/6/2016 10:49 AM	Rate (1)
Jeff Casagrande Posts: 1529 Rating: (202)	What are you using to drive the motor on your conveyor or feed roll? Motor with drive or simple contactor control?
Jeff Casagrande Posts: 1529 Rating: (202)
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3/6/2016 5:39 PM	Rate (0)
William_B Posts: 5225 Rating: (1194)	Hi Team, Much conversation has taken place.. good! Thank you Kal and Jeff for your contributions. First to keep with the original topic and @Pyrus: 1. Encoder wiring Your employer can handle the wiring of the encoder. Using quadrature (A/B phase) mode is important to you. And yes.. keep to that. Many methods are available to convert open-collector to PNP. One should be careful for not distorting the encoder pulse. A pull-up resistor or negating buffer is the most simple. Go ahead and use <Kal.A> recommendations - it is what I do. ---- 2. Code: Target reached As mentioned --\| == \|-- will cause problems. Very good - you have correctly identified why. (A) You could simply use --\| >= \|-- to counter the problem. The "BUT" in this are: * Reset the HSC to zero at the start of each length feed. You can use the CTRL_HSC to do this zeroing (reset). * The requested length should not be more than +MAX (+2147483647) of what DINT can give. * The "error" you make in your measurement should not influence the process. (B) The alternative is configuring interrupt routines as <Kal.A> explained. A good solution which I rarely follow. Triggering of physical outputs rarely benefits the accurate trigger. Being fair.. I also use multiple triggers which is a pain to configure. (C) If you are not zeroing the HSC then you have to employ another idea. (Code segments in SCL for ease of text.. LAD also possible) Before beginning feed: (triggered once per feed) startPosition := myHSC; //start position is captured endPosition := startPosition + targetDistance //calculate end position While running the evaluation is done: positionReached := (endPosition - myHSC) <= 0; ----- Now we are morphing to what your application requires. What follows next is not to the original topic,,,,,, w
William_B Posts: 5225 Rating: (1194)
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3/6/2016 5:39 PM	Rate (0)
William_B Posts: 5225 Rating: (1194)	Jeff Casagrande What are you using to drive the motor on your conveyor or feed roll? Motor with drive or simple contactor control? dummies!! crash test dummies! What happens to a crash head dummy when the test car is brought to an abrupt stop by a simulated accident. The momentum of the moving dummy pushes forward and comes to an end by seat belt / air bags / front window. Even with a single sheet of paper, this will be a problem. Now keep this in mind and read again Mr. Jeff's notes and read between the lines. Mr. Jeff is the authority on this subject. All the complications that Mr. Jeff and I have in mind may not apply to you. Now we get to the point where understanding the design is key. At this moment I think the design of your machine is flawed. But without design description (pictures), I may be wrong. Your descriptions up to now is not enough to fill in details. At the very least the feed should decelerate in a controlled way. Applying the brakes would be bad on so many levels.. it is uncontrolled - think crash test dummies. Even worse when having a stack of paper. Then we come to the blade that does the cutting. There is techniques employed when cutting through a stack of paper. If not done right, the blade will go blunt very quickly. Next.. The shape, blade material composition, and hardening plays as much a role as "sharpening" the blade. What influences the program? * movement control of the paper.. soft start and stop * prediction model for triggering a stop early as to come to standstill at the right place. Non-linearity can be expected on AC motors and drives. * Smarter control on how cutting action takes place. Now we get into a space where I am more hesitant to help. Doing system designs is what I am paid to do. I may alert you to some dangers but I am careful to not dictate solutions. The next step for you would be to absorb this info. Go to your employer and have a chat with him. If he gives you clear instructions on what to code.. then that is what you do (your risk is reduced). Else return here with more details on your system. What are your thoughts? w
William_B Posts: 5225 Rating: (1194)
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3/7/2016 1:12 AM	Rate (0)
Pyrus Advanced Member Joined: 10/8/2015 Last visit: 9/5/2024 Posts: 62 Rating: (3)	Wow... This really isn't as simple (in system design) as I thought it would be. The problems are slowly being revealed like moths to a flame, and it worries me. I don't even know what the speed of the motor is, o consider if the breaking system would indeed be safe or not. Exactly as you guys mentioned: "Crash test dummies". Specially if there are stacks of paper, they will definitely fall in given at a high speed. What I'm thinking about is motion control. I do hope this works though. I will have to define an offset to the counter so that the motor stops on its own, due to the weight of the papers. Let's say (depending on the size) it should be 1500 pulses, I'll give it an offset of 100 pulses, so that it reaches 1400 (and due to some inertia, may cross a bit a more, but that is to be expected). Now, the next step that I'm thinking is always using comparison instructions so that the motor slowly and with many triggers and stops covers the last pulses it's supposed to cover. For example: Let's say it reached 1462 pulses. 38 pulses remaining. I use comparison instruction to give immediate start and stop responses to the motor so that it covers the needed pulses. I'll put multiple stops for most possible accuracy, and the data to compare will always be updated ones from a global data block in which the counter value is. So, 10 + 10 +10 +5 + 2 +1... Meaning I'll need a comparison instruction for 10 pulses, 5 pulses, 2 pulses and 1 pulse, each triggering the next if condition is true, otherwise it will keep on repeating. After all steps are complete, manual or automatic input may be executed to trigger the negative transition of the blade (when it cuts and goes back to its place) that indicates the cut is complete and the system is ready for another sequence. Now, I really am hoping that the motor is slow, in which case the breaking system may not be of much affect in shock or sudden stop forces. I hope I am understanding you guys well, and taking the correct methods to solve this issue. The only thing I'm worried about is about an entire system change (should the client desires)... I do hope it does not come to that though

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3/7/2016 5:11 AM	Rate (0)
William_B Posts: 5225 Rating: (1194)	I don't care how good a hacker someone is - Without intense knowledge of the mechanics and physics involved in the project, the code has a high chance of failing. Jeff Casagrande What are you using to drive the motor on your conveyor or feed roll? Motor with drive or simple contactor control? Mr. Jeff summed it up very nicely.. straight to the point. If you do have speed control ability but keep the AC motor then the following will be helpful: https://support.industry.siemens.com/cs/ww/en/view/24104802 more specifically... https://support.industry.siemens.com/cs/attachments/24104802/Set22_DocTech_Rt_V1d0_en.pdf Also.. https://support.industry.siemens.com/cs/ww/en/view/21063595 These articles aims on using the previous generation's S7-200. It would be easier to use the Siemens provided library and S7-200. Coding for the S7-1200 is possible by working with the theory that is detailed in the documents. w
William_B Posts: 5225 Rating: (1194)
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3/7/2016 7:27 AM	Rate (1)
Jeff Casagrande Posts: 1529 Rating: (202)	Pyrus Wow... This really isn't as simple (in system design) as I thought it would be. The problems are slowly being revealed like moths to a flame, and it worries me. I don't even know what the speed of the motor is, o consider if the breaking system would indeed be safe or not. Exactly as you guys mentioned: "Crash test dummies". Specially if there are stacks of paper, they will definitely fall in given at a high speed. What I'm thinking about is motion control. I do hope this works though. I will have to define an offset to the counter so that the motor stops on its own, due to the weight of the papers. Let's say (depending on the size) it should be 1500 pulses, I'll give it an offset of 100 pulses, so that it reaches 1400 (and due to some inertia, may cross a bit a more, but that is to be expected). Now, the next step that I'm thinking is always using comparison instructions so that the motor slowly and with many triggers and stops covers the last pulses it's supposed to cover. For example: Let's say it reached 1462 pulses. 38 pulses remaining. I use comparison instruction to give immediate start and stop responses to the motor so that it covers the needed pulses. I'll put multiple stops for most possible accuracy, and the data to compare will always be updated ones from a global data block in which the counter value is. So, 10 + 10 +10 +5 + 2 +1... Meaning I'll need a comparison instruction for 10 pulses, 5 pulses, 2 pulses and 1 pulse, each triggering the next if condition is true, otherwise it will keep on repeating. After all steps are complete, manual or automatic input may be executed to trigger the negative transition of the blade (when it cuts and goes back to its place) that indicates the cut is complete and the system is ready for another sequence. Now, I really am hoping that the motor is slow, in which case the breaking system may not be of much affect in shock or sudden stop forces. I hope I am understanding you guys well, and taking the correct methods to solve this issue. The only thing I'm worried about is about an entire system change (should the client desires)... I do hope it does not come to that though I think you need to focus a little more on the system design at this point and a little less on how to process encoder signals. That will turn out to be the simple part. You need to know how you are moving the product. If you have a drive system, and if you have an encoder on the motor, then the built in Motion functions should work fine for what you are doing. Depending on your tolerance and dynamic requirements, a standard AC should work fine. Use your other encoder to measure the actual length and close your position loop. Use In_Position and 0_Speed signals to control your shear. Brake really is not needed except for holding with no power.
Jeff Casagrande Posts: 1529 Rating: (202)
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3/25/2016 9:10 PM	Rate (1)
Pyrus Advanced Member Joined: 10/8/2015 Last visit: 9/5/2024 Posts: 62 Rating: (3)	Hello again! I just wanted to log in to tell you that the encoder with the program worked! Believe it or not, I STILL didn't see the client's machine to take the proper measurements to know the factor to multiply with (or divide) depending on the high speed counter. I put a suggestive constant (x100 multiply) and making it the goal of the high speed counter. (Basically, if I need 25 (units), the encoder has to count 2500 pulses to reach). I have also manually created an automatic position control to control those extra counts the motor includes due to inertia when the power should be off. The HMI and PLC code both are working perfectly. Thank you all for your help! Strangely enough, when I did the online simulation, there was no need for a cable shield or anything. It worked out on its own. Dunno how exactly. I just used 2 wires for power, and 2 wires for the A/B quadrature phase.

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11/13/2017 9:29 PM	Rate (0)
Jeremy Miller Member Joined: 4/28/2015 Last visit: 2/25/2024 Posts: 3 Rating: (0)	You will only need to hook up the following provided that the inputs are open, and using HSC 1 enabled. A+ to I0.0 B+ to I0.1 Then monitor ID1000 under the HSC, Dont forget to change your input channel 0 and 1 filters to the respected rate of your encoder.

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11/14/2017 12:31 PM	Rate (0)
Piotr.M Platinum Member Joined: 6/24/2013 Last visit: 10/31/2024 Posts: 1645 Rating: (422)	this is an perfect example why I hate FBD ;-) it looks like a web and I think after a year you will not be able to understand what the thing is about! you need write code in a way others can understand and follow it EASILY for your own benefit and for benefit of your service / maintenance staff!

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